1/3 cup white or rice vinegar
4 tbsp brown sugar
1 tbsp ketchup
1 tsp soy sauce
2 tsp cornstarch (mixed with 4 tsp water)
1. Mix the vinegar, brown sugar, ketchup, and soy sauce together, and bring to a boil in a small pot.
2. Dissolve the cornstarch to water, add to the other ingredients and stir to thicken.